1. Field of the Invention
The present invention pertains to providing locatable identification of non-metallic secreted objects and continuous lines and more particularly to providing and to locating non-metallic objects, such as buried plastic pipe so that they can easily be located and their path traced without disturbing the objects.
2. Description of the Related Art
In general, identification of buried non-metallic objects, such as duct pipe and fiber optic transmission lines, include magnetic lines located helically around non-metallic ducts to identify non-metallic objects buried beneath the surface. Almost all provide for an elongated magnetic device that is magnetized transverse to its length. The following patents represent the state of the art in providing magnetic type of identification for buried objects or transmission lines.
U.S. Pat. No. 5,006,806, titled "Methods and Apparatus Employing Permanent Magnets for Marking, Locating, Tracing and Identifying Hidden Objects Such as Buried Fiber Optic Cables", issued to John B. Rippingale, et al. relates to providing elongated permanent magnet identifier devices having magnetic fields that may be detected at a distance from the objects. In one embodiment the identifier device comprises an elongated strip magnetized in the direction of its width and formed into a long pitch helix, producing a characteristic "magnetic field signature" that enhances detection and identification of the object, as by a portable gradiometer that is moved over the surface of the earth along a line generally parallel to the length of the object. This embodiment may provide a magnetic field that diminishes as the square of the distance from the identifier device (rather than the usual cube of the distance,) thereby enabling detection at substantial distances. In a second embodiment, distinctive magnetic field signatures are produced by arrays of spaced permanent magnets, the fields of which add and subtract to provide resultant magnetic fields with both peaks and valleys along a line generally parallel to the length of the object.
U.S. Pat. No. 5,051,034, titled "Magnetically Detectable Plastic Pipe," issued to William G. Goodman, relates to a magnetically detectable plastic pipe, such as polyethylene, polyvinyl, etc., for underground use that includes a hollow tubular plastic pipe having particles of magnetic material embedded in plastic and secured integrally with the wall of the pipe. The magnetic particles are of iron oxide or barium ferrite and of a size, shape, distribution and proportion such that the plastic pipe may be easily detected by magnetic detection apparatus on the surface when the plastic pipe is buried at a selected depth under the ground. The magnetic particles are uniformly distributed throughout the thickness and uniformly distributed around the entire circumference of the plastic pipe, or the magnetic particles may be distributed in discrete portions of the plastic pipe, as for example, a uniform outer layer of the pipe, or in stripes or strips extending along the pipe. The particles may be extruded with the plastic in forming the pipe, whether uniformly dispersed or in discrete regions, or the pipe may be formed of plastic free of the magnetic particles and the magnetic particles provided in a layer separately adhered to the wall of the pipe. The magnetic strips or magnetic portions of the plastic pipe may have selected areas or portions magnetized to encode information readable from the surface of the ground above the buried pipe or in inventorying pipe on the surface.
U.S. Pat. No. 5,321,361, titled "Apparatus and Method for Directing Magnetically Detectable Plastic Pipe and Other Sources of Magnetic Fields From a Distance Using a Vertically Aligned Gradiometer on a Horizontal Support," issued to William G. Goodman, relates to an apparatus for manipulation by an operator or user for detecting magnetically detectable plastic pipe and other sources of magnetic fields from a distance. This apparatus has a horizontally oriented support member with a handle extending at an acute angle therefrom. A magnetic field gradiometer comprising a hollow non-magnetic tube with two flux gate magnetometers therein is supported at the distal end of the support member a substantial distance ahead of the operator in a substantially vertical position. The support member includes a microprocessor operatively connected through a differential amplifier to the gradiometer for processing signals therefrom. An electronic read out module is supported on the handle spaced from the gradiometer and operable to receive signals from the microprocessor and convert them into an audible or visual display to be sensed by the operator or user. The size and weight distribution of the apparatus and the angles at which the components are assembled assure that when the apparatus is hand held by the handle the gradiometer is balanced in a vertical position at a substantial distance ahead of the operator or user. An alternate embodiment, a magnetic field mapper, is illustrated having a plurality of gradiometers supported in parallel on supporting wheels and having the visual and audio display in the form of a laptop or notebook type computer supported on the handle for the wheeled apparatus. A hand held embodiment of the mapper is also discussed.